Recently, miniaturization of memory hard disk drives and high storage memory capacity for memory hard disk drives have been demanded. In order to increase the recording density, it has been urged to lower the flying height of a magnetic head and to reduce the unit recording area. In addition, even for the manufacturing step of a magnetic disk substrate, the necessary requirements of the surface qualities of the substrate after polishing have become more severe every year. In order to satisfy the lowering of the flying height of the magnetic head, surface roughness, microwaviness, and projections have been required to be reduced. In addition, in order to increase the recording area per single hard disk, planarization has been required even to an edge portion of the circumference of the substrate, so that it has been important to suppress roll-off (edge-rounding) during polishing of a substrate.
WO 98/21289 discloses a polishing composition containing an oxyalkylene alkyl sulfate, but the reduction in roll-off cannot be said to be sufficient. JP2004-179294 A discloses a polishing composition containing an aromatic sulfonic acid or a salt thereof for a technique of polishing a semiconductor, but the reduction in roll-off is insufficient due to the combination with a weak acid. Similarly, JP2005-167231 A discloses a polishing composition containing an alkylaromatic sulfonic acid or a salt thereof for a technique of polishing a semiconductor, but the reduction in roll-off cannot be accomplished because the polishing composition is weakly acidic or basic.